This patch tries to fix the problem of page fault exception caused byaccessing nmiaction structure in nmi if kmemcheck is enabled.

If kmemcheck is enabled, the memory allocated through slab are in pagesthat are marked non-present, so that some checks could be done in thepage fault handling code ( e.g. whether the memory is read beforewritten to ). As nmiaction is allocated in this way, so it resides in a non-presentpage. Then there is a page fault while the nmi code accessing thenmiaction structure, which would then cause a warning byWARN_ON_ONCE(in_nmi()) in kmemcheck_fault(), called by do_page_fault().